Add to ORKGWe present a decentralized-control methodology and a tool-set for developing interactive user interfaces. We focus on the common case of developing the client side of Web applications. Our approach is to combine vi-sual programming using Google Blockly with a single-threaded implementation of behavioral programming in JavaScript. We show how the behavioral program-ming principles can be implemented with minimal pro-gramming resources, i.e., with a single-threaded envi-ronment using coroutines. We give initial, yet full, ex-amples of how behavioral programming is instrumental in addressing common issues in this application do-main, e.g., that it facilitates separation of graphical rep-resentation from logic and handling of complex inter-obje...